The present invention relates in general to the devices and methods for cleaning and archiving of used lithographic plates having pre-formed peripheral edge flanges and in particular to a lithographic plate washing method and apparatus for the facilitated automatic washing and rinsing of previously used lithographic plate members having substantially flat central portions and pre-formed parallel flanged peripheral edges.
Modern web and sheet-feed lithographic printing is done through the use of metal plates having pre-formed flanges formed in their peripheral edges so as to enable them to be wrapped around and held by the cylinder of a printing press and thereby used for printing by rotary methods. As a rule, the images upon the plates are not printed directly from the plate on to the paper, but are first transferred to an intermediate rubber cylinder which then transfers or "offsets"the image to the paper. Since grease and water are normally mutually repellent, ink is applied to ink receptive oleophyllic treated printing areas of a lithographic plate, while the non-printing parts, which absorb and hold water (i.e. the hydrophyllic areas), reject the greasy ink.
Once these lithographic plates are used, the conventional method through which they are "reprocessed" or cleaned for reuse involves a removal from the archiving area, and the preliminary removal of gum arabic sealant which has been previously placed on the plate to prevent moisture damage due to oxidation during storage since the images to be printed are normally photographically exposed to a light sensitive coating on the material. The gum arabic sealant is normally applied right over the ink residue and contaminants, thereby requiring the normally laborious hand operation of "hand scrubbing" the unsealed plate over a down draft sink with DUMAKLEEN brand solvent or the like and sponges.
The prior art has included apparata such as the Kodak polymatic plate processor (Model No. 48A) which, among other things, apply rotary scrubbing operations to lithographic plates. Devices such as Harris U.S. Pat. No. 580,312, Bendedict, U.S. Pat. No. 1,072,902 and Lakeman, U.S. Pat. No. 1,633,216 have employed one or more brushes to clean plates, as well. Lakeman '216 further employs a perforated solvent sprayer rod. Lindquist, Pat. No. 2,726,414 includes brushes, rollers and other apparata for washing, cleaning and drying lithographic plates.
Swindler, U.S. Pat. No. 2,926,371 employs a brush treatment system with interrupted rollers for treating the edges of bent sheets of laminated safety glass. Conrad et al., U.S. Pat. No. 3,479,852 provides for the treatment of strip metal with special edge forming elements. Savort, U.S. Pat. No. 3,382,520 includes separate rinse tanks for the treatment of offset printing plates. Casson, Jr., U.S. Pat. No. 3,682,079 is another plate developing apparatus employing feed rollers for conveying, and which applies developing solution, applies a rinse to the plate, and has developer and rinse tanks. Casson '079 also applies gumming solution to the plates.
Drawbacks have been encountered with lithographic plate processors such as the above-described prior art. In particular, such conventional devices present problems in maintaining the pre-formed peripheral edge flanges in the plate members during the processing thereof. Moreover, the present aforementioned method of "hand scrubbing" the plate members prior to reuse thereof, is unacceptably laborious and time consuming.
Hence, the present invention has as an object the facilitating of more effectively cleaning such used lithographic plate members.
Moreover, the present invention has as an object the providing of substantially automatic and continuous feeding into the apparatus, dispensing of cleaning solvent onto the plate, scrubbing, rinsing and removal from the apparatus while accommodating and preserving the peripheral pre-formed flanges formed of the plate members.
The present invention has the further object of providing an economical way of recycling the relatively costly cleaning solvent for reapplication and reuse in the apparatus.
The present invention has the further object of increasing the cost-effectiveness of archiving used lithographic plate members for future reuse.
These and other objects of the invention will become apparent in light of the present specification, drawings and claims.